The present invention relates to seesaw switches, and more particularly to the contact structure of such a switch wherein the movable contact piece is securely held in place and yet it can move smoothly between its various positions.
Seesaw switches are, of course, known and are typically used to switch power in industrial devices and audio equipment, and the like.
FIG. 1 is an explanatory view of the contact structure of a known seesaw switch. In the figure, numeral 11 designates a casing and a receiver 14 having a U-shaped section is fixed to the bottom surface 11a of the casing. The receiver 14 is adapted to hold a movable contact piece 16 for rocking movement between two stationary terminals 15 each having a stationary contact 15a and disposed on respective sides of the casing. The receiver 14 is fixed to a middle terminal 12 by a rivet 13 and movable contacts 16a are provided at respective ends of the movable contact piece 16, which is formed substantially in the shape of the letter V. Numeral 17 indicates a driving rod which is disposed so as to come into sliding contact with the facing surface 16b of the movable contact piece 16, and which is received through a coiled spring 18 in a hole provided in a driving member, not shown, rockably supported by the casing 11. The movable contact piece 16 is held to the receiver 14 in a manner allowing it to be rocked in the direction of arrows by the protuberant pieces 14a formed at the upper ends of the receiver 14 and held in engagement with slots 16c provided centrally of the contact piece 16.
The switching operation of such switches is carried out as stated below. In the initial state, i.e. neutral position, the fore end of the driving rod 17 lies over the center of the middle terminal 12 and is in resilient contact with the upper surface 16b of the movable contact piece 16. The movable contact piece 16 is supported at two points by the receiver 14. Therefore, the movable contacts 16a on respective sides of the contact piece are equally distant from the respectively corresponding stationary contacts 15a, and the switching circuit is open. When the driving member is rocked from its neutral position, the driving rod 17 begins to move rightward of leftward from its central position. When the fore end of the driving rod 17 passes over one free end 14b of the receiver 14, the movable contact piece 16 is instantly and suddenly inclined about the fulcrum formed by the free end 14b by the resilient force of the coiled spring 18. Thus, a movable contact 16a is moved into engagement with a stationary contact 15a, and the switching circuit is closed.
In such seesaw switches, the movable contact piece 16 is held to the receiver 14 by the protuberant pieces 14a of the receiver 14 being fitted within the slots 16c. This has led to the disadvantage that, upon the sudden inclination of one side of the movable contact piece 16, the other side tends to rise due to the impact, with the result that the slots 16c of that other side may rise out of engagement with the protuberant pieces 14a. In order to prevent the movable contact piece 16 from lifting off the receiver 14, the height of the protuberant pieces 14a of the receiver 14 have been increased. With this method, however, the width of the slots 16c must be broadended so as not to hinder the turning of the movable contact piece 16. The enlarged width increases the play of the movable contact piece 16 in the longitudinal direction thereof. This play has led to the disadvantage that the movable contact 16a undergoes a positional deviation relative the stationary contact 15a and that the contacts do not touch normally in an extreme case, especially when the switch is used with higher voltage and thus the contact gaps are large, so the performance becomes unstable.